Oscillation generation



Feb. 6, 1934. G, E: PRAY 1,945,547

OSCILLAT ION GENERAT ION Original Filed May 31, 1930 2 Sheets-Sheet 1 a r i F r 2" i i i i l i l l F l l I T 'I' ATTORNEY Feb. 6, 1934. Y 1,945,547

050 ILLAT I ON GENERAT I ON Original Filed May 31, 1930 2 Sheets-Sheet 2 TPrrn l flafll ly Ira 220617; i /04 a4 4 I I T firm all?! 'er 7 INVENTOR G. E. PRAY W ATTORNEY Patented Feb. 6, 1934 UNITED STATES OSCILLATION GENERATION George Emerson Pray, Wading River, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 31, 1930, Serial No. 457,897 Renewed February 7, 1933 20 Claims. (Cl. 179-171) This invention relates to oscillation generation and especially to a system wherein a single long line is utilized for frequency control and stabilization.

In the copending application of James L. Finch and James W. Conklin, Serial Number 363,660, filed May 16, 1929, in the United States Patent Office, a frequency control system is described wherein the frequency of an electron emission tube oscillator is frequency controlled and stabilized accurately by the use of a long, aperiodic, line associated with the input and output circuits of the oscillator. By making the line a whole number of half wave lengths long, and, in the case of a single electron discharge device, an odd number of half wave lengths long, potentials appearing in the output circuit of the device or oscillator are transferred to the input or control electrode thereof a time later such that anode and control electrode alternating voltages are 180 degrees out of phase. As this is the correct phase relationship for sustained oscillation generation, and since this relationship is not obtained for energy of frequencies other than that for which the line is the correct number of half wave lengths long, the system becomes frequency discriminating and produces oscillations only at a frequency corresponding to that for which the line produces the 180 degree phase change in grid and anode voltages.

The line as described has been found especially useful in transmitters for controlling the frequency of oscillation thereof and offers many advantages; namely, it makes the frequency of oscillation independent of biasing potentials applied to the oscillator, independent of variations in tuning, variations in load, and, in addition,

. since the line can be made to handle large amounts a desired frequency. To overcome the foregoing I difficulty is one of the objects of my present invention and I accomplish it by providing switching means associated with a plurality of rela tively fixed taps on a long line whereby a single line can be used for the control, at a plurality of different frequencies, of an oscillation generator.

Still another object of this invention is to provide an arrangement wherein a single long line may be used for the simultaneous frequency control of a plurality of oscillators operating at different frequencies. I fulfill this object by connecting, at various points along. the length of a long line corresponding to the different frequencies for which it is desired that the line frequency stabilize various oscillators, surge impedances, preferably in the form of tuned circuits tuned to the different frequencies. I then utilize portions of the line up to the respective surge impedances for the control of the respective oscillators.

Still another object of the present invention is to provide a single long line for the control, at different bands of natural frequencies situated at or beyond the extreme frequencies of a desired frequency range, of two electron discharge devices or electron emission tube oscillators coupled to a common circuit and forced to oscillate at some common intermediate frequency. By oppositely varying the plate current of the oscillators, the intensity of energy supplied by each oscillator is varied and as a. result the common frequency shifts towards the frequency of that oscillator supplying the greater amount of energy.

In this manner, frequency modulated energy within a predetermined band of frequencies may be obtained.

My invention is more fully described in connection with the accompanying drawings wherein Figure 1 illustrates one form of my invention teaching the utilization of a single long line for controlling, at one of any of several desired frequencies, the frequency of oscillation of an oscillator,

Figure 2 is a modification of Figure 1 wherein a single long line is utilized to simultaneously control, at different frequencies, the frequency of a plurality of independent oscillators,

Figure 3 illustrates the use of a long line for fixing the natural frequencies of two electron emission tube oscillators, at or beyond the extreme frequencies of a predetermined range, forced to oscillate together at a common intermediate frequency, and

Figure 4 is a modification of Figure 3 wherein modulation energy is applied to the screen grids of the oscillators.

Turning to Figure 1, assume that it is desired that electron emission tube oscillator 2 having a single long line frequency control means 4, be operated at one of a plurality of predetermined frequencies. To do so, according to my inven- 110 tion, I place on line 4, shielded by grounded shielding means 6, a plurality of relatively stationary taps 8, 10 and 12.

, As disclosed in the copending application of James L. Finch and James W. Conklin referred to, the long line 4 may be made in any form so as to be electrically long and yet physically small, the simplest being a properly shielded coil. As shown, the input end 14 of the line is coupled to the output or tunable tank circuit 16 of electron discharge device 2 and blocked from the source of unidirectional anode potential by a suitable blocking condenser 18. To obtain suitable biasing potential for the control electrode 20 of tube 2, a grid leak and condenser arrangement 22 of suitable design or any other suitable biasing method may be provided in which case an audiofrequency by-passing condenser should be provided to replace the alternative form of biasing means in the form of biasing battery 56.

Point 8 on the line is connected through suitable switching means 24 and circuit 26, either a resistance equal in value to the surge impedance of line 4 or, preferably, a tuned circuit tuned to a frequency such that for the frequency determined by the tap 8, the impedance which circuit 26 offers to the line is equal to the surge 1mpedance of long line 4, thus making it aperiodic at that frequency.

Similar'remarks are applicable to tunable circuits 28, 30 which are tuned so that, at the frequencies corresponding to tapping points 10, 12, respectively, they present to the long lme an 1mpedance equal to the surge impedance of the line. Of course, any one or more of the tunable circuits may be replaced by resistanceshaving a value equal to the surge impedance of lme 4.

Moreover, assuming that it is desired to transmit relatively long wave length energy, tap is switched into circuit, making the length of line included between the input and output circuits of electron discharge device 2 an effective odd number of half wave lengths long, the wave length taken corresponding to the desired frequency. Accordingly, for that frequency, when a relatively positive voltage appears at the input tapping point 32 of long line 4, a relatively negative potential appears at point 8 and is transferred through switching means 24 conductor 34 and switching means 36, to the control electrode '20 of oscillator 2. Similarly, with a negative voltage appearing at point 32, a relatively positive potential is applied to the control electrode 20; and, in this fashion the long line 4 frequency stabilizes the system for a frequency determined by tapping point 8.

To control the amount of energy fed back, tapping point 32 is made adjustable on the inductance coil forming part of the tank or output circuit 16.

If it is desired that oscillations be generated at a higher frequency, for example, the frequency for which there is an odd number, of half wave lengths between relatively stationary tapping point 10 and point 14 of line 4, switching means 24 and 36 are moved over to their mid positions. The tuning of tank circuit 16 is similarly altered to the new frequency. In order to facilitate adjustments, a uni-control means 38 comprising suitable mechanical linkage or gearing or both, is provided for simultaneously moving switching means 24, switching means 36 and for adjusting the tuning of tank circuit 16.

In the mid position, energy is transferred from the output circuit of electron discharge device 2 to point 10, switching means 24,'line 40 and through circuit 28 and blocking condenser 42 to ground. Input oscillator energy is applied through conductor 44, in the mid position of the system, through switching means 36 to the control electrode 20 of vacuum tube 2.

For a still higher frequency the uni-control means is manipulated so that tapping point 12 and impedance matching circuit 30 come into play for controlling the frequency of oscillation of oscillator 2.- Of course, the number of tapping points and corresponding circuits may be altered at will and if desired, one or more resistors of proper value may be used in place of all of the impedance matching circuits.

The oscillations generated may be modulated by applying modulated energy from source 46 through transformer 48 to the control electrode of vacuum tube 2 as shown, or if desired, to electrode 58, or '72. Radio frequency choke 50 and resistance 54 are provided to prevent the flow of radio frequency currents through the modulating circuits. Biasing potential may alternately be supplied to the control electrode 20 from a source of potential 56. To prevent feed back through the interelectrode capacity of tube 2, tube 2 is preferably of the screen grid type having a screen grid 58 grounded by suitable condenser 60 for radio frequency energy. Output energy from the tube may be radiated through a suitable antenna 62, or fed into a power amplifier, coupled in any suitable fashion to the tank circuit 16.

The parallel tuned circuits shown in Figure 1 may be replaced by series tuned circuits. In that case, no switching is necessary; for, the tank circuit tuning togetherwith the characteristics of the tuned series circuits will act to incorporate, for frequnecy control, only the proper length of line corresponding to the tuning of the tank circuit 16. The connection would be similar to that shown in, Figure 2 with the exception that all of the series tuned circuits would be parallel between an electrode of a single oscillator and ground.

Figure 2 distinguishes over Figure l in providing a single long line for frequency controlling a plurality of oscillators operating at different frequencies. Here, a plurality of oscillators 2, 2' and 2" preferably of the type shown in Figure 1 have tank circuits 16, 16' and 16" tuned to different desired frequencies. Any number of oscillators and associated tank circuits may, of course, be provided. Feed back from tank circuit 16 to its corresponding oscillator is through blocking condenser 64, conductor 66 and thence to long line 4. The long line is properly terminated for the frequency represented by the tuning of tank circuit 16 by a series tuned circuit 68 which, at that frequency presents a surge impedance corresponding to the surge impedance of line 4.

For a frequency corresponding to the tuning 16' or tank circuit 16" corresponding portions of the line 4 are included between the output circuits and the relatively stationary taps 10, 12. The line at the frequency 16' is properly terminated by another series tuned circuit, or, if desired a resistance having an impedance equal to the surge impedance of line 4. Similar remarks are applicable for feed back of energy of a frequency corresponding to the tuning of tank circuit 16".

In the foregoing manner portions of line 4 are included between the input and output circuits of each of the oscillators 2, 2', 2" corresponding to the frequency at which it is desired that each oscillator oscillate. Energy is predominant in each oscillator at that frequency for which the tank circuit is tuned and for which one of the tapping points 8, 10, 12 has been adjusted; for, due to the fact that energy at the other frequencies will appear in incorrect phase relationship and due to the impedance characteristics of the various circuits involved, practically no energy of the other frequencies will appear in the oscillators taken separately. Modulation may be accomplished in, and output may be derived from, each of the oscillators in the manner similar to that disclosed in connection with Figure 1.

My invention as disc osed in Figures 1 and 2 may be applied to a frequency modulation transmitter of the type shown in Figure 3. Here, signaling currents are amplified by a suitable amplifier and applied in pushpull-fashion or in phase opposition to the control electrodes, to the screen grids, or to the plates of oscillators 82, 84 thereby varying the intensity of oscillations supplied by each oscillator to the common output circuit 86, the frequency of energy in which fluctuates. and depends upon the intensity of the energy supplied by each oscillator. In the absence of modulating energy, both oscillators oscillate at a common frequency fixed at an intermediate point in the range of frequencies through which it is desired that they operate. The natural frequency of oscillator 82 is determined by the portion of line 4 included between tapping point 88 and by-pass condenser 90. Similarly, the natural frequency of oscillation of oscillator 84 is determined by the portion of line included between its anode circuit, or, condenser 90 and relatively fixed tapping point 92. Because the two oscillators have a common tank circuit tuned preferably to an intermediate, com mon, frequency, they are forced to oscillate at the intermediate frequency, and, they will oscillate at some other frequency only when the plate current of the oscillators is relatively oppositely varied or wobbled by the modulation currents.

To suitably terminate the line 4 so that no reflections appear thereon and so that the transfer of energy from the output circuit to the input circuits of the oscillators is substantially aperiodic, impedances 94, 96 either in the form of resistances or tuned circuits having impedances at the respective frequencies equal to the surge impedance of the line 4, are provided. As in the case of Figure 1 and Figure 2 the screen grids of oscillators 82, 84 are grounded through suitable condenser 60. Suitable screen grid biasing potential is provided through the action of resistance 98.

Frequency wobbled energy appearing in the output circuits 86 of oscillators 82, 84 may be directly transmitted or radiated or fed, as indicated, to a power amplifier 100 and then transmitted or radiated over a suitable antenna 102, or, if desired over land lines or cables.

If desired, modulation may be accomplished by variation in screen grid voltage as shown in Figure 4. Modulating energy is fed to two modulator tubes 104 which have a common output resistor 106, the voltages across which, due to variation in plate current through the modulator tubes, control the amount of energy supplied to tank circuit 86 by the oscillators 82, 84.

A similar scheme could be used for modulation of the plate voltage of the oscillators, in which case, radio frequency choke coils should be placed in the leads from resistor 106 to the anodes of the oscillators. The high voltage connection for the anodes of the oscillators, shown in Figure 4, would, of course, be omitted for plate voltage modulation.

Having thus described my invention, what I claim is:

1. In combination, a single long line, a single electron discharge device oscillator having its anode coupled at one point to the long line, a plurality of surge impedances connected between different points on the line and ground, and means for establishing connection between each surge impedance and the control electrode of the oscillator.

2. The combination of an electron discharge device oscillator, a long line several half wave lengths long at the operating frequency for controlling the frequency of oscillation thereof, and switching means operatively connected with a plurality of relatively stationary taps on said line for controlling the frequency at which the line stabilizes the frequencyof the oscillator.

3. In combination, an electron discharge device oscillator, a long line several half wave lengths long at the operating frequency between the input and output circuits thereof, relatively stationary taps along the length of the line to vary the length of line included between the input and output circuits of the electron discharge device, and switching means for choosing at will without disturbing the taps, the length of line to be so included.

4. In radio signaling apparatus, an electron discharge device oscillator, a long line for controlling the frequency ofoscillations generated thereby, a plurality of taps on the line to control the effective portion of the line included in circuit with the oscillator to control the frequency of oscillations generated thereby, a plurality of tuned circuits tuned to the differentfrequencies of electrical energy to be transferred by the line, switching means between the line taps and tuned circuits, and switching means between the tuned circuits and the input circuit of said electron discharge device oscillator.

5. In radio signaling apparatus, an electron discharge device oscillator, a long line for controlling the frequency of oscillations generated thereby, a plurality of taps on the line to control the effective portion of the line included in circuit with the oscillator for controlling the frequency of oscillations generated thereby, a plurality of tuned circuits tuned to the different frequencies of electrical energy to be transferred by the line, switching means between the line taps and tuned circuits, switching means between the tuned circuits and the input circuit of said electron discharge device oscillator, and means for operating said switching means simul taneously.

6. In combination, in radio signaling apparatus, a plurality of electron discharge device oscillators, means for roughly fixing, at different frequencies, the frequency of each oscillator and, a single long line operatively connected with all of the oscillators for simultaneously fixing accurately at said different frequencies, the frequency of oscillation of the oscillators.

7. In combination, a long aperiodic line, a plurality of electron discharge device oscillators having their anodes coupled at one point to the long aperiodic line, a plurality of surge impedances connected between different points on the line and ground, and connections between the surge impedances and the control electrodes of the oscillators.

8. In radio signaling apparatus, the combination of a single long aperiodic line, a plurality of electron discharge devices having their anodes coupled to the single long aperiodic line, a plurality of tuned circuits .tuned to different frequencies connected between the line and ground, and, a connection between one of said tuned circuits and the control electrode of one of said oscillator tubes.

9. An arrangement for controlling the fre quency of oscillation over a. desired range comprising two sources of alternating electrical energy having different natural frequencies, a single long line for fixing the frequencies ator beyond the extreme frequencies of the desired range, a common circuit fed from both of said sources and means for varying the relative intensity of the energy supplied from each of said sources in order to vary the frequency of the energy appearing in the common circuit.

10. An arrangement for controlling oscillation frequency over a desired range comprising two electron emission tube oscillation generators, a single long line for fixing their natural frequencies to or beyond the extreme frequencies of a desired range, means coupling the oscillation generators together to force them to oscillate at a common frequency, and means for changing the relative intensity of the oscillations generated in each generator in order to control their common frequency.

11. An arrangement for controlling oscillation frequency overa desired range comprising two regeneratively coupled electron emission tube generators, a single long line for establishing feed back 'for the generators arranged so as to maintain the oscillations generated by each tube at or beyond the extreme frequencies of a desired range, means coupling the oscillation generators together to force them to oscillate at a common frequency, and means for oppositely changing the bias of the control electrodes of the tubes to vary the intensity of the oscillations of each generator in order to control their common frequency.

12. An arrangement for generating frequency wobbled energy comprising two electron emission tube generators having natural frequencies fixed to or beyond extreme frequencies of a desired range of frequency wobble, a single long aperiodic line for fixing their natural frequencies, means coupling'the generators together to force them to oscillate at a common frequency, and means for simultaneously oppositely wobbling the bias of the control electrodes of the tubes to oppositely vary oscillation intensity in order to wobble I the common frequency.

electron discharge device, a long transmission line coupled to said electron discharge device, and means forv simultaneously varying the tuning of said circuit and the effective length of said transmission line.

15. In apparatus for undulatory electrical currents, an electron discharge device, a tunable circuit coupled thereto for approximately controlling the frequency of operation of said electron discharge device, a long transmission line coupled to said device for increasing the frequency selectivity of said tunable circuit and said device, and, means for simultaneously varying the electrical length of said transmission line and the tuning of said tunable circuit.

16. An oscillation generator comprising an electron discharge device having an anode a cathode and a control electrode, a circuit tuned, to approximately a desired operating frequency connected between said anode and cathode, a long transmission line connected between said anode and control electrode, and, a series tuned circuit comprising an inductance coil and a condenser serially connected together connected between the control grid end of said line .and said cathode.

1'7. Apparatus as claimed in the preceding claim wherein means are provided for reducing the effects of anode control grid capacity.

18. An oscillation generator' comprising an electron discharge device having an anode a cathode and a control electrode, a long transmission line a plurality of half wave lengths long connected at one end to said anode, a serially tuned circuit connected between the other end of said transmission line and said cathode, and, a parallel tuned circuit connected between said anode and cathode, said parallel tuned circuit being tuned to approximately a desired frequency of operation.

19. An oscillation generator comprising an electron discharge device having an anode a cathode and a control electrode, a circuit tuned to approximately a desired operating frequency connected between said anode and cathode, a long transmission line connected between said anode and said control electrode, and means for simultaneously varying the tuning of said circuit and the effective length of said line connected between said anode and control electrode.

20. Apparatus as claimed in the preceding claim wherein said means for simultaneously altering the length of said line and the tuning of said circuit also simultaneously changes the value of impedance connected between the output end of said line and said cathode.

G. EMERSON PRAY. 

